JP5323372B2 - Cathode coating for wet electrolytic capacitors - Google Patents

Abstract

A wet electrolytic capacitor that comprises an anode, cathode, and working electrolyte is provided. The cathode contains a coating disposed over a surface of a current collector, wherein the coating comprises a plurality of electrochemically-active particles and a binder. The binder is formed from an amorphous polymer having a glass transition temperature of about 100° C. or more.

Description

  Electrolytic capacitors are increasingly being used in many circuit designs because of their volumetric efficiency, reliability, and process compatibility. Electrolytic capacitors typically have a higher capacity per unit volume than some other types of capacitors, making them valuable for use in relatively high current, low frequency electrical circuits. One type of capacitor that has been developed is a wet electrolytic capacitor, which includes an anode, a cathode current collector (eg, an aluminum can), and a liquid or “wet” electrolyte. Wet electrolytic capacitors tend to provide a good combination of high capacity and low leakage current. In some situations, wet electrolytic capacitors can exhibit advantages over solid electrolytic capacitors. For example, a wet electrolytic capacitor can operate at a higher operating voltage than a solid electrolytic capacitor. Furthermore, wet electrolytic capacitors are often larger in size than solid electrolytic capacitors, resulting in higher capacitance values.

  In an effort to further improve the electrical performance of wet electrolytic capacitors, carbon powder is often deposited on the cathode current collector. Unfortunately, it is difficult to directly bond carbon powder to some types of current collectors. Accordingly, various techniques for solving this problem have been developed. For example, Matsumoto et al. US Pat. No. 6,914,768 describes a technique for depositing a carbonaceous layer on a cathode current collector. This layer includes a carbonaceous material, a conductive agent, and a binder material. The binder material can assist in attaching the carbonaceous material to the surface of the current collector, but nevertheless the ability to block the pores and surface of the carbonaceous material and thereby increase the effective cathode surface area. Is considered to limit.

  Although the benefits achieved by conventional wet electrolytic capacitors are many, there is a need for further improvements.

  According to one embodiment of the present invention, a wet electrolytic capacitor is disclosed that includes an anode, a cathode, and a working electrolyte. The cathode includes a coating disposed on the surface of the current collector, the coating including a plurality of electrochemically active particles and a binder. The binder is formed from an amorphous polymer having a glass transition temperature of about 100 ° C. or higher.

  Other features and aspects of the present invention are described in detail below with reference to the accompanying drawings.

  As will be apparent to those skilled in the art, the following description is merely illustrative and is not intended to limit the invention in any way.

The present invention relates to a wet electrolytic capacitor including an anode, a cathode, and an electrolyte disposed therebetween. Specifically, the cathode is formed from a coating disposed on the current collector. The cathode current collector shall be formed from any metal suitable for use in forming capacitors such as tantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver, steel (eg, stainless steel), alloys thereof, and the like. You can also. The form of the cathode current collector can generally be varied as is known in the art. For example, the current collector can be in the shape of a container, can, foil, sheet, foam, mesh, screen, cloth, felt or the like. In one embodiment, the cathode current collector is a mesh material. The surface area of the cathode current collector is selected to obtain a certain level of capacity. For example, the cathode current collector has a surface area of from about 0.1 to about 25 cm ² , in some embodiments from about 0.2 to about 15 cm ² , and in some embodiments from about 0.5 to about 10 cm ^2. To cover. It should be understood that the specific surface area of the current collector can be much larger than the range described above.

The cathode coating is formed from conductive electrochemically active particles so that the electrolyte maintains good electrical contact with the cathode current collector. The magnitude of the conductivity can be expressed as the “specific resistance” of the electrochemically active particles at about 20 ° C., which is typically less than about 1 Ω · cm, and in one embodiment about 1 × 10 ⁻ Less than ² Ω · cm, in one embodiment less than about 1 × 10 ⁻³ Ω · cm, and in one embodiment less than about 1 × 10 ⁻⁴ Ω · cm. The electrochemically active particles increase the effective cathode surface area through which the electrolyte is in electrochemical communication with the cathode current collector. By increasing the effective cathode surface area in this manner, a capacitor with increased cathode capacity for a given size and / or reduced size for a given capacity can be formed. Typically, the electrochemically active particles are at least about 200 m ² / g, in some embodiments at least about 500 m ² / g, and in some embodiments at least about 1500 m ² / g. Specific surface area. In order to obtain the desired surface area, the size of the electrochemically active particles is generally small. For example, the intermediate size of the electrochemically active particles is less than about 100 μm, in some embodiments from about 1 to about 50 μm, and in some embodiments from about 5 to about 20 μm. Similarly, the electrochemically active particles can be porous. Without wishing to be bound by theory, it is believed that the porous particles provide a path for the electrolyte to provide good contact with the cathode current collector. For example, the electrochemically active particles have pores / channels having an average diameter greater than about 5 angstroms, in some embodiments greater than about 20 angstroms, and in some embodiments greater than about 50 angstroms. Can do.

Any of a variety of electrochemically active particles can be used. For example, as electrochemically active particles, formed from ruthenium, iridium, nickel, rhodium, rhenium, cobalt, tungsten, manganese, tantalum, niobium, molybdenum, lead, titanium, platinum, palladium, osmium, and combinations of these metals Metals such as particles can be used. In one particular embodiment, for example, the electrochemically active particles are palladium particles. Non-insulating oxide particles can also be used in the present invention. Suitable oxides include metals selected from the group consisting of ruthenium, iridium, nickel, rhodium, rhenium, cobalt, tungsten, manganese, tantalum, niobium, molybdenum, lead, titanium, platinum, palladium, and osmium, and these Combinations of metals can be included. Particularly suitable metal oxides include ruthenium dioxide (RuO ₂ ) and manganese dioxide (MnO ₂ ). Carbonaceous particles such as activated carbon, carbon black, graphite, etc. having the desired conductivity level can also be used. Some suitable shapes of activated carbon and techniques for forming them are disclosed in Ivey et al. U.S. Pat.No. 5,726,118, Wellen et al. U.S. Pat.No. 5,858,911, and Shinozaki et al. U.S. Patent Application Publication No. 2003/0158342. Please refer to it.

  Because it is often difficult to bond electrochemically active particles directly to the cathode current collector, the cathode coatings of the present invention include within the cathode coating to assist in attaching the electrochemically active particles to the cathode current collector. An amorphous polymer binder is used. Many common binders are formed from an essentially semi-crystalline or crystalline thermoplastic polymer (eg, polytetrafluoroethylene). During the formation of the capacitor, these binders generally melt, thereby “wetting” a significant portion of the electrochemically active particles. In contrast, amorphous polymers having a relatively high “glass transition temperature” (“Tg”) do not dissolve as much as ordinary thermoplastic binders, leaving the particles uncovered. Thus, it is considered to act as an electrochemical interface between the electrolyte and the current collector, thereby increasing the capacity. Specifically, the amorphous polymers of the present invention generally have a temperature of about 100 ° C. or higher, in some embodiments about 150 ° C. or higher, and in some embodiments about It has a glass transition temperature of 250 ° C or higher. As is known, the glass transition temperature can be determined using differential calorimetry (“DSC”) according to ASTM D-3418.

Any of a variety of amorphous polymers having the desired glass transition temperature can be used in the present invention. One class of particularly suitable amorphous polymers are thermoplastic polyimides, which are typically aromatic bonds linked by imide linkages (ie, linkages in which two carbonyl groups are bonded to the same nitrogen atom). Includes a family ring. Suitable thermoplastic polyimides can include, for example, poly (amide-imide) available as Sollon ^™ from Solvay Polymers; poly (ether-imide) available as Ultem ^™ from GE Plastics; copolymers thereof, and the like. . The amide-imide polymer can be derived, for example, from an amide-amic acid polymer precursor. The polyamide-amic acid precursor is then thermally cured (typically at a temperature of about 150 ° C. or higher) to form a polyamide-imide. The polyamide-amic acid can be prepared by subjecting at least one polycarboxylic anhydride or derivative thereof and at least one first diamine to a condensation polymerization reaction. Specifically, the anhydride is typically a trimeric anhydride or a lower alkyl ester of a halogenated trimellitic acid (eg, acid chlorides of trimellitic anhydride, ie, chlorinated trimellitic anhydride (TMAC)). , Trimellitic acid or a derivative thereof. Similarly, the first diamine is typically p-phenylenediamine, m-phenylenediamine, oxybis (aniline), benzylene, 1,5-diaminonaphthalene, oxybis (2-methylaniline) 2,2-bis [4. -(P-aminophenoxy) phenyl] propane, bis [4- (p-aminophenoxy)] benzene, bis [4- (3-aminophenoxy)] benzene, 4,4′-methylenedianiline, or combinations thereof An aromatic diamine such as Examples of other useful aromatic primary diamines are disclosed in US Pat. No. 5,230,956 to Cole et al. And US Pat. No. 6,479,581 to Ireland et al. Particularly suitable aromatic diamines include meta-phenylenediamine and oxybis (aniline).

Although not required, the amorphous polymer binder can be supplied in the form of particles to enhance its adhesive properties. When using these binder particles, they typically have a size distribution ranging from about 1 to about 250 μm, and in some embodiments from about 5 to about 150 μm. For example, the particles may have a D ₉₀ particle size distribution of about 150 μm or less, in some embodiments about 100 μm or less, and in some embodiments about 75 μm or less (90% by weight of the Having a smaller diameter).

  The relative amounts of electrochemically active particles and binder within the cathode coating can be varied depending on the desired characteristics of the capacitor. For example, in general, increasing the relative amount of electrochemically active particles increases the cathode capacity of the capacitor. However, if the amount of electrochemically active particles is too large, the coupling between the cathode coating and the cathode current collector may be insufficient. Thus, to obtain an appropriate balance between these properties, the cathode coating is typically from about 0.5: 1 to about 100: 1, in some embodiments from about 1: 1 to about 50: 1. : 1, and in some embodiments, the electrochemically active particles and binder, respectively, in a weight ratio of about 2: 1 to about 20: 1. The electrochemically active particles may comprise from about 50% to about 99% by weight of the cathode coating, from about 60% to about 98% by weight in some embodiments, and about 70% by weight in some embodiments. % To about 95% by weight. Similarly, the binder comprises from about 1% to about 40% by weight of the cathode coating, in some embodiments from about 2% to about 30%, and in some embodiments about 5% by weight. Up to about 20% by weight.

  In addition to containing the electrochemically active particles and binder, the cathode coating can also contain some other elements. For example, in some embodiments, conductive fillers can be used to further increase the conductivity of the coating. These conductive fillers can be particularly beneficial in diminishing any loss of conductivity that can be caused by the binder covering a portion of the surface of the electrochemically active particles. Any suitable conductive filler such as metal particles (eg, silver, copper, nickel, aluminum, etc.); non-metal particles (eg, carbon black, graphite, etc.) can be used. If a conductive filler is used, it can represent from about 1% to about 40% by weight of the cathode coating, in some embodiments from about 2% to about 30%, and in some embodiments. From about 5% to about 20% by weight can be constituted.

  In order to deposit the coating on the cathode current collector, the electrochemically active particles, binder and / or conductive filler can be mixed separately or together with a solvent to produce a coating formulation. Water; glycols (eg, propylene glycol, butylene glycol, triethylene glycol, hexylene glycol, polyethylene glycol, ethoxydiglycol, and dipropylene glycol); glycol ethers (eg, methyl glycol ether, ethyl glycol ether, and isopropyl glycol ether) ); Ethers (eg, diethyl ether and tetrahydrofuran); alcohols (eg, methanol, ethanol, n-propanol, iso-propanol, and butanol); triglycerides; ketones (eg, acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters ( For example, ethyl acetate, butyl acetate, diethylene glycol ether acetate, and methoxypropyl acetate); amides For example, dimethylformamide, dimethylacetamide, dimethylcapryl / caprin fatty acid amide, and N-alkylpyrrolidone); nitriles (eg, acetonitrile, propionitrile, butyronitrile, and benzonitrile); sulfoxides or sulfones (eg, dimethylsulfoxide (DMSO)) , And sulfolane) and the like can be used. The concentration of the solvent can generally vary, but it is still typically from about 25% to about 95% by weight of the coating formulation, and in some embodiments from about 30% to about 90% by weight. And, in some embodiments, is present in an amount from about 40% to about 85% by weight.

In order to achieve the desired thickness of the coating, generally the solids and / or viscosity of the coating formulation can be varied as desired. For example, the solids content ranges from about 5 wt% to about 60 wt%, more specifically from about 10 wt% to about 50 wt%, more specifically from about 20 wt% to about 40 wt%. Can span. By changing the solid content of the coating formulation, the presence of particles in the coating can be controlled. For example, in order to form a cathode coating using higher levels of electrochemically active particles, the formulation can be provided with a relatively high solids so that a higher percentage of particles are incorporated into the coating during the deposition process. it can. Furthermore, the viscosity of the coating formulation can also be varied depending on the coating method and / or the type of solvent used. For example, a lower viscosity can be used for some coating techniques (eg, dip coating) and a higher viscosity can be used for other coating techniques. Generally speaking, the viscosity measured with a Brookfield DV-1 viscometer with an LV spindle is less than about 2 × 10 ⁶ centipoise, and in some embodiments, less than about 2 × 10 ⁵ centipoise, some embodiments Is less than about 2 × 10 ⁴ centipoise, and in some embodiments is less than about 2 × 10 ³ centipoise. If desired, thickeners or other viscosity modifiers can be used in the coating formulation to increase or decrease the viscosity.

  Once produced, the coating formulation can be applied to the cathode current collector using any known technique. For example, the cathode coating is deposited using techniques such as sputtering, screen printing, dipping, electrophoretic coating, electron beam deposition, spraying, roller pressing, brushing, doctor blade casting, centrifugal casting, masking, and vacuum deposition. Can be made. Other suitable techniques are disclosed in US Pat. No. 5,369,547 to Evans et al., US Pat. No. 6,594,140 to Evans et al., And US Pat. No. 6,224,985 to Shah et al. For example, the cathode current collector can be dipped in or sprayed with the coating formulation. The coating formulation can cover the entire surface of the current collector. Alternatively, the coating formulation can cover only a portion of the current collector so as to leave room for leads to the current collector. For example, the coating formulation can cover from about 25% to 100% of the surface of the current collector, and in some embodiments, from about 60% to 95% of the surface of the current collector. Once applied, the coating formulation can optionally be dried to remove any solvent. Drying can be performed, for example, at a temperature from about 50 ° C. to about 150 ° C.

  The cathode of the present invention is particularly suitable for wet electrolytic capacitors that include an anode, a cathode, and a working electrolyte disposed therebetween and in contact with the anode and cathode. In this regard, various embodiments of wet electrolytic capacitors that can be formed according to the present invention are described in detail below. It is to be understood that the following description is merely exemplary and that many other embodiments can be implemented by the present invention.

The anode can generally be formed from a variety of different materials. For example, the anode can be formed from a powder composed primarily of valve metal (ie, an oxidizable metal) or from a composition that includes the valve metal as an element. Suitable valve metals that can be used include, but are not limited to, tantalum, niobium, aluminum, hafnium, titanium, alloys of these metals, and the like. For example, the anode is formed of a valve metal oxide or nitride (eg, niobium oxide, tantalum oxide, tantalum nitride, niobium nitride, etc.) that is generally considered to be a semiconductive or highly conductive material. be able to. Valve metal oxides that are particularly suitable for use in the anode have an atomic ratio of niobium to oxygen of 1: <2.5, in some embodiments 1: <1.5, in some embodiments 1: <1.1, and slightly In this embodiment, niobium oxide of 1: 1.0 ± 0.2 is included. For example, the niobium oxide can be Nb _0.7 , NbO _1.0 , NbO _1.1 , and NbO ₂ . Another example of these valve metal oxides is disclosed in US Pat. No. 6,322,912 to Fife et al. Examples of valve metal nitrides appear on 20th March 20th, 2000, 20th Symposium on Capacitor and Resistance Technology, Newsletter of CARTS 2000, T. Tripp paper “Tantalum Nitride: A New Substrate for Solid Electrolytic Capacitors” It is disclosed.

In order to form the anode, a variety of common manufacturing procedures can generally be used. For example, the anode can be formed as a foil, pressed powder, etc., as is known in the art. Examples of pressed powder anodes are disclosed, for example, in US Pat. No. 7,099,143 to Fife et al. Alternatively, the anode can be formed from ceramic particles (eg, Nb ₂ O ₅ , Ta ₂ O ₅ ) that are chemically reduced to form a conductive material (eg, NbO, Ta). For example, a slip composition comprising ceramic particles can first be formed and deposited in the form of a thin layer on a substrate. If desired, multiple layers can be formed to achieve the target thickness of the anode. The formed layer or layers can be heat treated to chemically reduce the ceramic particles to form a conductive anode. These slip-formed anodes can provide small thickness, high aspect ratio (ie, width to thickness ratio), and uniform density (which can result in improved volume efficiency and equivalent series resistance (“ESR”)). ). For example, the anode can have a thickness of about 1500 μm or less, in some embodiments about 1000 μm or less, and in some embodiments about 50 to about 500 μm. Similarly, the anode can have an aspect ratio of about 1 or more, in some embodiments about 5 or more, and in some embodiments about 15 or more. An example of a slip-formed anode as described above is disclosed in the application “Anode for use in electrolytic capacitors” (Attorney No. X1P-0278) filed concurrently with this application.

  The anode can have any desired shape, such as square, rectangular, circular, oval, triangular, etc. Polygonal shapes having more than four sides (eg hexagonal, octagonal, heptagonal, pentagonal, etc.) are particularly desirable because of their relatively large surface area. The anode is “fluted” including one or more flutes, grooves, indentations, or indentations to increase the surface to volume ratio to minimize ESR and expand the frequency response of the capacity. ) Can also have a shape. Such "fluted" anodes are described, for example, in Webber et al. US Pat. No. 6,191,936, Maeda et al. US Pat. No. 5,949,639, Bourgault et al. US Pat. No. 3,345,545, and Hahn et al. Please refer to 2005/0270725.

Once formed, the anode can be anodized so that a dielectric film is formed on and within the anode. Anodization is an electrical and chemical process in which the anode metal is oxidized to form a material having a relatively high dielectric constant. For example, a niobium oxide (NbO) anode can be anodized to form niobium pentoxide (Nb ₂ O ₅ ). Specifically, in one embodiment, the niobium oxide anode is heated to a high temperature (eg, about 85 ° C. while supplying a controlled amount of voltage and current to form a niobium pentoxide coating having a thickness. ) In a weak acid solution (for example, phosphoric acid, polyphosphoric acid, a mixture thereof). The power supply is initially kept at a constant current until the required generated voltage is reached. The power supply is then held at a constant voltage so that the desired dielectric thickness is formed on the surface of the anode. The anodization voltage is typically in the range of about 10 to about 200V, and in some embodiments about 20 to about 100V. In addition to being formed on the surface of the anode, typically a portion of the dielectric oxide film is also formed on the surface of the pores of the material. It should be understood that the dielectric film can be formed from other types of materials and using different techniques.

  The working electrolyte is an electrically active material that provides a connection between the anode and the cathode, and is generally in the form of a liquid such as a solution (eg, aqueous or non-aqueous), dispersion, gel, etc. is there. For example, the working electrolyte can be an aqueous solution of an acid (eg, sulfuric acid, phosphoric acid, or nitric acid), a base (eg, potassium hydroxide), or a salt (eg, an ammonium salt such as nitrate), or in an organic solvent. It can also be any other suitable working electrolyte known in the art, such as a salt dissolved in (e.g., an ammonium salt dissolved in a glycol-based solution). A variety of other electrolytes are disclosed in US Pat. Nos. 5,369,547 and 6,594,140 to Evans et al.

  In one particular embodiment, the electrolyte is relatively neutral, from about 5.0 to about 8.0, in some embodiments from about 5.5 to about 7.5, and in some embodiments from about 6.0. It has a pH up to about 7.5. Although having a neutral pH level, the electrolyte is still conductive. For example, the electrolyte may be about 10 milliSiemens / centimeter (mS / cm) or more at a temperature of 25 ° C., in some embodiments about 30 mS / cm or more, and some embodiments. Can have a conductivity from about 40 mS / cm to about 100 mS / cm. This conductivity value can be measured by using a known conductivity meter (for example, Oakton Con series 11) at a temperature of 25 ° C.

  The working electrolyte can include various elements that help optimize the conductivity, pH, and stability of the capacitor during storage and use. For example, a solvent that generally functions as a carrier for other components of the electrolyte can be used. The solvent is about 30% to about 90% by weight of the electrolyte, about 40% to about 80% by weight in some embodiments, and about 45% to about 70% by weight in some embodiments. Can be configured. Water (eg, deionized water); ethers (eg, diethyl ether and tetrahydrofuran); alcohols (eg, methanol, ethanol, n-propanol, isopropanol, and butanol); triglycerides; ketones (eg, acetone, methyl ethyl ketone, and methyl isobutyl) Ketones); esters (eg, ethyl acetate, butyl acetate, diethylene glycol ether, methoxypropyl acetate); amides (eg, dimethylformamide, dimethylacetamide, dimethylcapryl / caprin fatty acid amide, and N-alkylpyrrolidone); nitriles (eg, Acetonitrile, propionitrile, butyronitrile, and benzonitrile); sulfoxides or sulfones (eg, dimethyl sulfoxide (DMSO), and It can be used any of various solvents such as sulfolane) and the like. Although not necessary, the use of an aqueous solvent (eg, water) is often desirable to help maintain the pH of the electrolyte at a relatively neutral level. In fact, water represents about 50% or more, in some embodiments about 70% or more, and in some embodiments, one or more solvents used in the electrolyte. Can constitute about 90 to 100% by weight.

  The conductivity of the working electrolyte is imparted by one or more ionic compounds (ie, compounds that contain one or more ions, or compounds that can form one or more ions in solution). can do. Suitable ionic compounds include, for example, inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc .; acrylic acid, methacrylic acid, malonic acid, succinic acid, salicylic acid, sulfosalicylic acid, adipine Acid, maleic acid, malic acid, oleic acid, gallic acid, tartaric acid, citric acid, formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid Organic acids including carboxylic acids such as itaconic acid, trifluoroacetic acid, barbituric acid, cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid; methanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, Trifluoromethanesulfonic acid, styrenesulfonic acid, naphthalene disulfonic acid, hydroxy Sulfonic acids such as benzene sulfonic acid; poly (acrylic) or poly (methacrylic) acid and copolymers thereof (eg maleic acrylic, sulfone acrylic, and styrene acrylic copolymers), carrageenic acid, carboxymethylcellulose, alginic acid, etc. Such polymer acids can be included. Acid anhydrides (eg, maleic anhydride) and salts of the acids mentioned above can also be used. Salts of metal salts such as sodium salt, potassium salt, calcium salt, cesium salt, zinc salt, copper salt, iron salt, aluminum salt, zirconium salt, lanthanum salt, yttrium salt, magnesium salt, strontium salt, cerium salt It can be in the form or in the form of a salt prepared by reacting an acid with an amine (eg, ammonia, triethylamine, tributylamine, piperazine, 2-methylpiperazine, polyallylamine).

  The concentration of the ionic compound is selected so as to obtain a desired balance between conductivity and pH. That is, the concentration is typically limited to maintain the desired neutral pH, but a strong acid (eg, phosphoric acid) can be used as the ionic compound. When a strong acid is used, it is usually from about 0.001% to about 5% by weight of the electrolyte, in some embodiments from about 0.01% to about 2%, and in some embodiments about 0.1% by weight. To about 1% by weight. On the other hand, a weak acid (eg, acetic acid) can be used if the desired conductivity is obtained. When weak acids are used, they are usually from about 1% to about 40% by weight of the electrolyte, in some embodiments from about 2% to about 30%, and in some embodiments about 5% by weight. % To about 25% by weight. If desired, a mixture of weak and strong acids can be used in the electrolyte. The total concentration of ionic compounds can vary, but typically is from about 1% to about 50% by weight of the electrolyte, in some embodiments from about 2% to about 40%, and slightly In this embodiment, it is about 5 wt% to about 30 wt%.

  If desired, an amount of a basic pH regulator effective to balance the effects of ionic compounds that affect pH can be used in the electrolyte. Suitable basic pH modifiers include, but are not limited to, ammonia; mono, di, and tri-alkyl amines; mono, di, and tri-alkanol amines; alkali metal and alkaline earth metal hydroxides; Metal and alkaline earth metal silicates; and mixtures thereof. Specific examples of basic pH modifiers are ammonia; sodium, potassium, and lithium hydroxide; sodium, potassium, and lithium metasilicates; monoethanolamine; triethylamine; isopropanolamine; diethanolamine; and triethanolamine. is there.

  In general, the freezing point should be about -20 ° C or lower, and in some embodiments about -25 ° C or lower, in order to keep the electrolyte stable during normal storage and use. Is desirable. If desired, glycols (eg, propylene glycol, butylene glycol, triethylene glycol, hexylene glycol, polyethylene glycol, ethoxydiglycol, dipropylene glycol, etc.); glycol ethers (eg, methyl glycol ether, ethyl glycol ether, isopropyl glycol) One or more freezing point depressants such as ethers etc. can be used. The concentration of the freezing point depressant can vary, but typically it is from about 5% to about 50% by weight of the electrolyte, in some embodiments from about 10% to about 40%, and slightly In this embodiment, it is present from about 20% to about 30% by weight. It should also be noted that the boiling point of the electrolyte is typically about 85 ° C. or higher, and in some embodiments about 100 ° C. or higher, so that the electrolyte remains stable at high temperatures.

  A depolarizing material can also be used in the working electrolyte to help control the hydrogen gas generation at the cathode of the electrolytic capacitor. (If the depolarizing material is not used, the capacitor will swell and eventually cause a failure. Can wake up). When using a depolarizer, it is typically from about 1 to about 500 ppm of electrolyte, in some embodiments from about 10 to about 200 ppm, and in some embodiments from about 20 to about 150 ppm. Configure.

  Suitable depolarizers are 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzonic acid, 3-nitrobenzonic acid, 4-nitrobenzonic acid, 2-nitroacetophenone, 3- Nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole, 3-nitroanisole, 4-nitroanisole, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, Nitroaromatic compounds such as 4-nitrobenzyl alcohol, 2-nitrophthalic acid, 3-nitrophthalic acid, 4-nitrophthalic acid and the like can be included. Particularly suitable nitroaromatic depolarizers are nitrobenzoic acids, their anhydrides or salts substituted with one or more alkyl groups (eg, methyl, ethyl, propyl, butyl, etc.). Specific examples of these alkyl-substituted nitrobenzoic acid compounds include, for example, 2-methyl-3-nitrobenzoic acid; 2-methyl-6-nitrobenzoic acid; 3-methyl-2-nitrobenzoic acid; 3-methyl- 4-nitrobenzoic acid; 3-methyl-6-nitrobenzoic acid; 4-methyl-3-nitrobenzoic acid; their anhydrides or salts. While not intending to be theoretically limited, alkyl-substituted nitrobenzoic acid compounds preferentially absorb electrochemically on the active surface of the cathode surface when the cathode potential reaches a low region or when the cell voltage is high. It is believed that it can then desorb into the electrolyte as the cathode potential increases or the cell voltage decreases. As such, these compounds are “electrochemically reversible”, which can provide improved suppression of hydrogen gas evolution.

  In addition to the elements described above, other optional elements can be used for the wet electrolytic capacitors. For example, a conductive polymer coating located on the current collector and / or cathode coating can be used. Suitable conductive polymers include, but are not limited to, polypyrrole; polythiophene such as poly (3,4-ethylenedioxythiophene) (PEDT); polyaniline; polyacetylene; poly-p-phenylene; and derivatives thereof. Can be included. The conductive polymer coating can also be formed from multiple conductive polymer layers. For example, the conductive polymer coating can include one layer formed from PEDT and another layer formed from polypyrrole.

  Although not required, the conductive polymer coating can further increase the effective capacitance of the capacitor. For example, when conducting monomers are polymerized, they typically take an amorphous, non-crystalline form, which appears somewhat like a web when viewed with a scanning electron microscope. This means that the resulting conductive polymer coating has a large surface area and therefore operates to somewhat increase the effective surface area of the current collector coated by the coating deposition. It should be understood that various methods can be used to apply the conductive polymer coating to the cathode coating. For example, techniques such as screen printing, dipping, electrophoretic coating, and spraying can be used to form the coating. In one embodiment, for example, the monomer used to form the conductive polymer (eg, PEDT) can be first mixed with the polymerization catalyst to form a dispersion. For example, one suitable polymerization catalyst is BAYTRON C (Bayer Corp.), which is iron (III) sulfonate toluene and n-butanol. BAYTRON C is a catalyst commercially available for BAYTRON M, which is 3,4-ethylenedioxythiophene, and PEDT monomer is also commercially available from Bayer Corporation. After the dispersion is formed, a coated cathode current collector can be immersed in the dispersion to form a conductive polymer. Alternatively, the catalyst and monomer can be deposited separately. In one embodiment, the catalyst can be dissolved in a solvent (eg, butanol) and then deposited as a dipping solution. While various methods have been described above, any other method of depositing a coating comprising a conductive polymer coating can be used. For example, other methods of depositing coatings containing one or more such conductive polymers are described in US Pat. No. 5,457,862 to Sakata et al., US Pat. No. 5,473,8503 to Sakata et al., US Pat. See US Pat. No. 5,729,428 and U.S. Pat. No. 5,812,367 to Kudoh et al.

  Optionally, a protective coating can be positioned between the conductive polymer coating and the cathode coating. It is believed that the protective coating can improve the mechanical stability of the interface between the conductive polymer coating and the cathode coating. The protective coating can be formed from a relatively insulating resinous material (natural or synthetic). Some resinous materials that can be used include, but are not limited to, polyurethane, polystyrene, esters of unsaturated or saturated fatty acids (eg, glycerides), and the like. For example, suitable fatty acid esters include, but are not limited to, esters of lauric acid, myristic acid, palmitic acid, stearic acid, eleostearic acid, oleic acid, linoleic acid, linolenic acid, alleuritic acid, cellophosphoric acid, etc. including. Esters of these fatty acids are particularly useful when used in relatively complex combinations to form “dry oils” that allow the resulting film to be rapidly polymerized into a stable layer. I understood. These drying oils can contain mono, di, and / or tri-glycerides, which have a glycerol backbone with 1, 2, and 3 fatty acyl residues to be esterified, respectively. Yes. For example, some suitable drying oils that can be used include, but are not limited to, olive oil, linseed oil, castor oil, tung oil, soybean oil, and shellac. Details of these and other protective coating materials are disclosed in US Pat. No. 6,674,635 to Fife et al.

As is well known, the physical arrangement of the capacitor's anode, cathode, and working electrolyte can generally be varied. For example, refer to FIG. One embodiment of the illustrated wet electrolytic capacitor 40 includes a working electrolyte 44 disposed between the anode 20 and the cathode 43. The anode 20 includes a dielectric film 21, and a wire 42 (for example, tantalum wire) is embedded therein. The cathode 43 is formed from a cathode current collector 41 and a cathode coating 44. In this embodiment, the cathode current collector 41 is in the shape of a cylindrical “can” with a lid. A seal 23 (for example, a glass / metal seal) that couples and seals the anode 20 to the cathode 43 can also be used. Although not shown, the capacitor 40 can also include a spacer (not shown) that stably holds the anode 20 in the cathode 43. The spacer can be made of plastic, for example, and can be a washer type. A separator (e.g., paper) can be positioned between the cathode and anode so that the anode and cathode are not in direct contact, and so that ionic current can flow from the working electrolyte 44 to both electrodes. Any material used as a known electrolytic inner separator can be used as the separator of the present invention. Examples include paper, plastic fiber, glass fiber, paper made from these fibers, porous membranes, and ion permeable materials (eg, Nafion ^™ ). Typically, the anode and cathode are separated by a distance from about 10 μm to about 1000 μm. In order to obtain an external connection, a metal wire (not shown) is attached to the cathode by spot welding.

  In the embodiment shown in FIG. 1, only a single anode and cathode current collector is used. However, multiple (eg, two or more) anode and / or cathode current collectors can be included in the capacitor to increase capacity. Use any number of anode and / or cathode current collectors, for example from 2 to 50, in some embodiments from 4 to 40, and in some embodiments from 6 to 30 Can do. In order to minimize assembly thickness for “low profile” applications, anode and cathode current collectors are also typically arranged in a one or two dimensional array. Please refer to FIG. For example, capacitor 200 includes an array 100 of three individual cathodes 64 and two individual anodes 65. In this particular embodiment, array 100 includes anodes and cathodes arranged in a row and a column, the anodes and cathodes having their top / bottom surfaces adjacent to each other to minimize assembly height. It is positioned. For example, the upper surface of the cathode, which is limited by its width (−x direction) and length (−y direction), is located close to the corresponding bottom surface of the anode. Alternatively, the anode and cathode can be placed “end-to-end” such that the back side of one capacitor is positioned in close proximity to either the front or back side of another capacitor. It should be understood that the anode and cathode do not extend in the same direction. For example, one cathode surface may be provided in a plane substantially perpendicular to the -x direction, while another cathode surface is provided in a plane substantially perpendicular to the -y direction. Can do. However, it is desirable to extend the anode / cathode in substantially the same direction.

  Individual anodes and cathodes are electrically connected to respective anode and cathode terminals to form an integrated capacitor assembly. The terminals serve as electrical connections for the capacitor assembly and help stabilize the individual anodes and cathodes from movement. Any conductive material such as conductive materials (eg, tantalum, niobium, copper, nickel, silver, zinc, tin, palladium, lead, aluminum, molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof) Can be used to form terminals. Particularly suitable conductive materials include, for example, nickel, niobium, and tantalum. The terminals can generally be arranged in any desired technique so that they are electrically isolated from each other and can accept individual capacitors. In FIG. 2, for example, each cathode 64 of the capacitor 200 includes a cathode lead wire (for example, tantalum wire) 72 commonly connected to the cathode terminal 172. Similarly, each anode 65 includes an anode lead (eg, tantalum wire) 62 that is commonly connected to the cathode terminal 162. Cathode lead 72 and anode lead 62 are electrically connected to terminals 172 and 162, respectively, using known techniques. For example, the lead can be connected to the terminal either directly (eg, laser welding, conductive adhesive, etc.) or via an additional conductive element (eg, metal). Separator 117 is also positioned between the cathode and anode, preventing direct contact between both electrodes and allowing ionic current to flow from working electrolyte 144 to both electrodes.

  If desired, the elements of capacitor 200 can be placed in container 119. The container may have any shape, but the illustrated container 119 has a cylindrical shape having a top 121 and a bottom 123. The top 121 of the container 119 is covered with a lid 125 and a seal member 127 (for example, rubber cork). Container 119 and / or top 125 may be any of a variety of conductive materials such as copper, nickel, silver, zinc, tin, palladium, lead, aluminum, molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof. Can be made from Terminals 162 and 172 extend through lid 125 and provide subsequent electrical connections. In order to ensure electrical separation between terminals 162 and 172, a conductive rod (eg, stainless steel, niobium, etc.) is provided that encapsulates the terminals in the area near lid 125.

  Partly because of its high conductivity, wet electrolytic capacitors can achieve excellent electrical properties. For example, the equivalent series resistance (“ESR”) (the magnitude that a capacitor operates like a resistor when charging and discharging in an electronic circuit) is about 1500 measured using a 2V bias and a 1V signal at a frequency of 1000 Hz. Less than mΩ, in some embodiments less than about 1000 mΩ, and in some embodiments less than about 500 mΩ. The electrolytic capacitor of the present invention can be used in various applications including, but not limited to, medical applications such as defibrillators, automotive applications, military applications such as radar systems, and the like. The electrolytic capacitor of the present invention can also be used in consumer electronics such as radio and television.

  In the following, the invention will be described with reference to some examples, so that the invention can be better understood.

Example 1
First, a ceramic body was formed from the following composition.
Material weight%
Deionized (DI) water 19.05
Nonionic surfactant 0.19
Anionic polymer dispersant 1.30
Acrylic binder 9.76
Nb ₂ O ₅ powder 69.70

These ingredients were ground in a special M-18 vibratory mill. The composition formed was degassed by stirring in a slip pot for 24 hours. The slip was cast as a 0.001875 inch (1.875 mil) tape on a polypropylene carrier. The carrier with wet tape was floated on a water bath maintained at a constant temperature of 50 ° C. for 2 minutes to promote drying. At the end of the drying phase, a metal blade was used to separate the cast tape from the carrier and the tape was wrapped with a single paper sheet to prevent sticking of the tapes during tape storage. A 6 "x 6" piece was cut from the tape. Nine of these pieces of tape were stacked together and held together at 3000 psi in a press for 10 seconds. Sacrificial material was woven into the loom and placed between two 9-layer stacks. The sacrificial member was formed from Shakespeare WN-101 fishing line (0.0083 inch diameter). The stacked layers and room were then pressed together in a Shinto press at a pressure of 209 kg / cm ² for 18 seconds. Disconnect the pressed pad from the room, then press in the Clifton press at 1845 psi for 2 seconds to release from pressure, press at 1845 psi for 4 seconds to release from pressure, and so on, then press at 1845 psi for 16 seconds Laminated. The laminated pad was diced into 21.2 mm x 12.7 mm pieces using a PTC CC-7100 dicer. The thickness of the diced body was 0.7 mm. Each diced body weighed 0.55 g.

Example 2
A wet electrolytic capacitor was formed from the ceramic body of Example 1. First, a stainless steel mesh (150 × 150 mesh obtained from McMaster) was cut into a 2.2 cm × 1.1 cm rectangle. The cathode lead (150 μm gauge annealed stainless steel 304 wire) was cut to a length of 2.5 cm. These rectangles and wires were first washed in an ultrasonic bath using soap water at 45 ° C. for 30 minutes and then rinsed 4 times with deionized (“DI”) water. After drying in an 85 ° C. oven for 30 minutes, the sample was again defatted in ambient temperature acetone for 20 minutes. The sample was dried in an 85 ° C. oven to remove any residual acetone, rinsed 5 times with DI water, and then dried in an 85 ° C. oven. The cathode lead wire was welded to the center of the 1.1 cm side of the rectangular mesh using a spot welder. The depth was about 1.0 mm. The rectangular mesh was then etched in a solution of 1.0% by volume H ₂ SO ₄ and 0.1% by volume HCl for 1 minute, degreased 45 times with DI water, and then dried at ambient temperature using a blower. . The resulting mesh substrate had a thickness of about 130 μm.

  The ink was prepared by mixing 12.0 g N-methylpyrrolidone (NMP) and 4.0 g Norit DL C Super 30 activated carbon in a beaker using a magnetic stirrer. As a conductive filler, 0.4 g of BP2000 carbon black was added. Next, 0.5 g of Torlon TF 4000 (Solvay Advanced Polymers Co.) was added. Continuous mixing was continued for over 12 hours at ambient temperature. This ink was applied to a stainless steel substrate by dip coating. A spatula was used to scrape excess ink on both sides of the substrate to prevent the bottom coating from becoming thick. These wet cathodes were pre-dried at 120 ° C. for 15 minutes and then thermally cured at 260 ° C. for 30 minutes. The loading was 0.0107 g and the thickness was 150 μm.

For electrical measurements, a simple capacitor was assembled using one rectangular NbO anode for two cathodes. The anode was formed by placing the anode body of Example 1 on a porous Al ₂ O ₅ substrate. The bodies were then heated with 800 ° C. air for 60 minutes. The part with the binder removed was placed flat between two tantalum substrates (0.1875 inch thick) and heated at 1200 ° C. for 120 minutes in a hydrogen atmosphere. A 0.19 mm Ta wire was then inserted into the hole left by the nylon wire. The wire was bonded to the body by heating the part in vacuum at 1300 ° C. for 30 minutes. The anode was then anodized at 25 V in a general phosphoric acid bath at 85 ° C. to form a dense oxide dielectric. These rectangular anodes were 20.0 mm long, 11.0 mm wide and 0.7 mm thick. After stacking one anode, two cathodes, and two separators together, a piece of Scotch tape was used to wrap around the assembly. The separator was formed from KP 60 paper (MH Technologies Co.), which had a thickness of 18 μm, a length of 2.3 cm, a width of 1.2 cm, and a dielectric strength of 23.6 V / μm.

  Two cathode leads were welded to the cathode to minimize contact resistance. The anode-separator-cathode assembly was vacuum impregnated in an aqueous solution prepared according to the composition in Table 1 below for 30 minutes.

Table 1 Composition and properties of working electrolyte

An EG & G 273 potentiostat / galvanostat and Solartron 1255 frequency response analyzer (FRA) were used. Communication between the hardware and the electrochemical cell was done through Screibner Corrware 2.1 software. The impedance measurement of the wet anode / separator / cathode assembly was performed by controlling the bias to 2.0 V, 5.0 V, and 8.0 V, respectively, within a frequency frame from 0.1 Hz to 100,000 Hz. The real part of the Nyquist plot represents the equivalent series resistance (ESR) at a given frequency, and the imaginary part was used to calculate the capacity using the following equation:
C = 1 / (2 × π × f × Z ″)
However,
C: Capacity (F)
f: Frequency (Hz)
Z ": Imaginary part of impedance (Ω)
It is.

  The capacity measured at 0.1 Hz was used to approximate the capacity under DC conditions. It was 2.53 mF, 2.37 mF, and 2.31 mF at 2.0V, 5.0V, and 8.0V bias, respectively. ESR was evaluated at a frequency of 1000 Hz, but was independent of bias, unlike capacitance. It maintained about 1.0Ω for all biases.

The cathode was measured separately in a three-electrode system using the cyclic voltammetry method. The counter electrode was a 5.0 cm ² platinum mesh and the reference electrode was a saturated calomel electrode (SCE). The cathode potential was scanned between -0.5 V vs. SCE and 0.5 V vs. SCE at a rate of 25 mV / s. The direct current capacity of the cathode was calculated by the following formula.
C = ΔQ / ΔU
However,
C: Cathode capacity Q: Charge U: Cathode potential.

  The cathode capacity was estimated to be 558.7 mF, which is more than 200 times the anode capacity.

Example 3
Capacitors were formed as described in Example 2. However, carbon black was not used in the cathode ink. The resulting cathode loading was 0.0107 g. The capacitance measured at 0.1 Hz was 2.57 mF, 2.42 mF, and 2.37 mF for 2.0V, 5.0V, and 8.0V bias, respectively. The ESR was 1.98Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 550.0 mF.

Example 4
Capacitors were formed as described in Example 2. However, 1.0 g of Torlon TF 4000 was added. The cathode loading was 0.0113 g. The capacitance measured at 0.1 Hz was 2.54 mF, 2.41 mF, and 2.35 mF for biases of 2.0V, 5.0V, and 8.0V, respectively. The ESR was 1.35Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 550.0 mF.

Example 5
Capacitors were formed as described in Example 2. However, 0.4 g of acetylene carbon (Chevron) was used as the conductive filler. The cathode loading was 0.0060 g. The capacitance measured at 0.1 Hz was 2.60 mF, 2.36 mF, and 2.23 mF for biases of 2.0V, 5.0V, and 8.0V, respectively. The ESR was 1.15Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 500.0 mF.

Example 6
Capacitors were formed as described in Example 5. However, the stainless steel mesh was SS Monel 304 120 × 120 mesh. The cathode loading was 0.0074 g. The capacitance measured at 0.1 Hz was 2.64 mF, 2.46 mF, and 2.39 mF for biases of 2.0V, 5.0V, and 8.0V, respectively. The ESR was 1.24Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 403.4 mF.

Example 7
Capacitors were formed as described in Example 6. However, the stainless steel mesh was SS Monel 316 150 × 150 mesh. The capacitance measured at 0.1 Hz was 2.69 mF, 2.47 mF, and 2.37 mF for biases of 2.0V, 5.0V, and 8.0V, respectively. The ESR was 1.24Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 384.9 mF.

Example 8
Capacitors were formed as described in Example 5. However, the cathode substrate was 110 PPI (Inco) nickel foam. The cathode loading was 0.013 g. The capacitance measured at 0.1 Hz was 2.66 mF, 2.37 mF, and 2.28 mF for biases of 2.0V, 5.0V, and 8.0V, respectively. The ESR was 1.13Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 1250 mF.

Example 9
Capacitors were formed as described in Example 7. However, 0.4 g of BP2000 carbon black was used as the conductive filler. The cathode loading was 0.074 g. The capacitance measured at 0.1 Hz was 2.54 mF, 2.38 mF, and 2.32 mF for biases of 2.0V, 5.0V, and 8.0V, respectively. The ESR was 1.16Ω at a frequency of 1000 Hz. The cathode capacity was estimated to be 372.3 mF.

Example 10
Ten pieces of NbO anode, 11 pieces of cathode, and 20 pieces of separator paper were prepared as described in Example 2 and stacked in the order of cathode, separator, and anode. Each rectangular anode had a length of 11.0 mm, a width of 11.0 mm, and a thickness of 0.7 mm. The cathode was also cut to 11.0 mm square to match the anode size. A separator paper of the same size as in Example 2 was simply folded into a U shape and wrapped around an anode piece. The anode lead and the cathode lead were drawn from the stack in opposite directions. The entire stack was wrapped with Scotch tape. The tantalum lead wire for the anode and the stainless steel lead wire for the cathode were all trimmed to a length of 6.0 mm. The anode lead was welded to one heavy gauge stainless steel wire with a diameter of 0.2 mm and the cathode lead was welded to another wire. The thickness of the stack was 10.0 mm. The anode-separator-cathode assembly was vacuum impregnated in the aqueous electrolyte used in Example 2 for 30 minutes. The capacitance measured at 0.1 Hz was 14.53 mF, 12.84 mF, and 12.34 mF for biases of 2.0 V, 5.0 V, and 8.0 V, respectively. The ESR at a frequency of 1000 Hz was 0.22Ω.

Example 11
The anode and cathode were prepared as described in Example 2, but the dimensions were slightly changed. That is, the anode and cathode substrates were cut into 1.0 cm square. Separator paper of the same size as in Example 2 was folded into a U shape and wrapped around the anode. As shown in FIG. 2, two NbO anodes were stacked horizontally with three cathodes. The anode tantalum lead and cathode stainless steel lead were trimmed to a length of 6.0 mm. Using a laser welder and under argon atmosphere protection, the anode tantalum lead was welded to a 0.2 mm diameter heavy gauge tantalum wire and the cathode stainless steel lead was welded to a heavy gauge stainless steel wire. Both heavy gauge wires were welded to niobium rods using a spot welder. A nickel lead was then welded to these niobium rods. The assembly was then wrapped with Scotch tape to increase compression and vacuum impregnated for 30 minutes in the working electrolyte (described in Table 2 below) before being inserted into the case.

  The case and rubber cork were diverted from a Nichicon VZ 16V-10 mF leaded aluminum electrolytic capacitor and washed first in detergent and then in acetone to remove residual chemicals. The outer diameter of the cylindrical aluminum case was 18.0 mm and the height was 30.0 mm. The element was then used for packaging wet NbO capacitors. Since the aluminum case was used only as a container and not as an anode or cathode, its inner surface was masked with tape to prevent direct contact with the anode / cathode assembly. An absorbent cotton ball was placed on the bottom of the case and then presaturated with 2.5 g working electrolyte. After inserting the electrode assembly into the case, the case was immediately crimped using a lathe. The life test was performed for 2000 hours by applying a rated voltage of 16 V at 85 ° C.

  For the test, two working electrolytes shown in Table 2 below were prepared.

Table 2 Working electrolyte for wet NbO component life test

  There was no sign of precipitation in any electrolyte even after a thermal cycle of -30 ° C to 105 ° C. The results of the life test are shown in Table 3 below.

Table 3 Life test results

  As is apparent from Table 3, the difference in concentration of the gassing inhibitor (3-methyl-4-nitrobenzoic acid) does not significantly affect the initial performance of these capacitors. However, the capacitor using the electrolyte B exhibited extremely stable electrical characteristics even after 2000 hours when a rated voltage of 16 V was applied at 85 ° C., and was not damaged by the generation of gas. Capacitors using Electrolyte A containing a low concentration of gassing inhibitor failed as a result of case expansion caused by gas evolution in the early stages of the life test. Therefore, in order to extend the service life, the concentration of the gas generation inhibitor can be maintained at a relatively high level.

Example 12
The anode and cathode were prepared as described in Example 2. The anode was sliced into a 5.16 mm × 3.88 mm × 0.58 mm rectangle. Two different forming electrolytes were used to form these anodes. The electrolyte was a mixture of 1.0 wt% H ₃ PO ₄ (phosphoric acid) and 0.5 wt% H ₃ PO ₄ +0.5 wt% H ₅ PO ₄ (polyphosphoric acid). These anodes were first anodized at 24V, 85 ° C for 120 minutes. Some anodes were later passed through vacuum annealing and / or a second formulation as shown in Table 1. The capacities were determined by measuring the DC cell capacity of these anodes relative to the large Ta slag cathode in electrolyte B described in Example 11 using a galvanostatic charge / discharge method. The leakage current was measured in 1.0 wt% H ₃ PO ₄ . The normalized leakage current at 85 ° C. was calculated using the DC capacity at a bias of 2.0V and the leakage current measured 2 hours after applying the rated voltage of 16V. The results are shown in Table 4 below.

Table 4 Conditions and results of anodizing treatment and / or vacuum annealing

  As can be seen from the table, the anode formed in the phosphoric acid bath exhibited greater leakage current than the anode formed in the phosphoric acid and polyphosphoric acid mixture.

  Those skilled in the art will be able to make these and other modifications and variations of the present invention without departing from the spirit and scope of the invention. Further, it should be understood that aspects of the various embodiments may be interchanged in whole or in part. Further, those skilled in the art will appreciate that the above description is illustrative only and is not intended to limit the invention.

It is sectional drawing of one Embodiment of the capacitor | condenser by this invention. FIG. 6 is a cross-sectional view of another embodiment of a capacitor according to the present invention.

Explanation of symbols

20 Anode 21 Dielectric film 23 Seal 40 Capacitor 41 Cathode current collector 42 Anode lead wire 43 Cathode 44 Working electrolyte 62 Anode lead wire 64 Cathode 65 Anode 72 Cathode lead wire 100 Anode array 117 Separator 119 Container 121 Top of container 123 Bottom 125 Lid 127 Seal member 144 Working electrolyte 162 Anode terminal 172 Cathode terminal 175 Conductive rod 200 Capacitor

Claims (11)

A wet electrolytic capacitor,
An anode comprising tantalum, niobium, or a conductive oxide thereof;
A cathode comprising a coating disposed on the surface of the current collector;
Including
The coating covers the entire surface of the current collector, the coating includes a plurality of electrochemically active particles and a binder, wherein the binder is formed from an amorphous polymer having a glass transition temperature of 100 ° C. or higher. The amorphous polymer is a thermoplastic polyimide and the binder has a particle shape with a D ₉₀ particle size distribution of 150 micrometers or less;
A working electrolyte disposed between the cathode and the anode, further comprising a working electrolyte comprising an aqueous solution containing an acid;
A wet electrolytic capacitor characterized by that.   The wet electrolytic capacitor according to claim 1, wherein the amorphous polymer has a glass transition temperature of 150 ° C. or higher.   The wet electrolytic capacitor according to claim 1, wherein the polyimide is poly (amide-imide), poly (ether-imide), or a combination thereof.   4. The wet electrolytic capacitor according to claim 3, wherein the polyimide is poly (amide-imide) formed from trimellitic acid or a derivative thereof and an aromatic diamine. The wet electrolytic capacitor according to any one of claims 1 to 4, wherein the binder has a shape of particles having a _D90 particle size distribution of 75 micrometers or less.   The wet electrolytic capacitor according to any one of claims 1 to 5, wherein the electrochemically active particles are metal, metal oxide, carbonaceous particles, or a combination thereof.   The wet electrolytic capacitor according to claim 1, wherein the electrochemically active particles include activated carbon.   The wet electrolytic capacitor according to claim 1, wherein the coating further includes a conductive filler.   The wet electrolytic capacitor according to claim 1, wherein the anode includes a conductive oxide of tantalum or niobium.   The wet electrolytic capacitor according to claim 1, wherein the anode includes a dielectric film formed on and inside the anode by an anodic oxidation treatment of the anode.   The wet electrolytic capacitor according to claim 10, wherein the anode includes a conductive oxide of niobium, and the dielectric film includes niobium pentoxide.

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